Answer:
As a new covalent connection develops between the two glucose molecules, one loses a H group, the other loses an OH group, and a water molecule is freed.
Why does glucose form a polymer despite being a stable molecule?
The formation of glucose polymers (glycogen, starch, cellulose) requires the input of energy from uridine triphosphate (UTP). Any tiny molecules must be converted into bigger molecules, which is compatible with the second rule of thermodynamics. Building proteins from amino acids, nucleic acids from nucleotides, fatty acids and cholesterol from acetyl groups, and so on are examples. Energy is released when bigger molecules are broken down into smaller ones, which is compatible with the second rule of thermodynamics. Thus, glucose may be converted to CO2 and H2O, resulting in the production of ATP. While glucose is a tiny molecule and hence relatively "stable," it can exist at a potential energy level and may be used to build up (needs energy) or broken down (produces energy). All of these biochemical processes require the use of enzymes; otherwise, the activation energy of most reactions would require extremely long periods of time for random energy inputs to push the reactions in either direction, despite the fact that energy considerations favor spontaneous breakdown over synthesis.